GLLIGHT

NAME

C SPECIFICATION

void f3glLightffP(
GLenum fIlightfP,

GLenum fIpnamefP,
GLint fIparamfP )

delim $$

PARAMETERS

f2lightfP

Specifies a light.
The number of lights depends on the implementation,
but at least eight lights are supported.
They are identified by symbolic names of the form %f3GL_LIGHTfP$i$
where 0 (<= $ i $ < %f3GL_MAX_LIGHTSfP.

Specifies the value that parameter f2pnamefP of light source f2lightfP
will be set to.

C SPECIFICATION

void f3glLightfvfP(
GLenum fIlightfP,

GLenum fIpnamefP,
const GLint fI*paramsfP )

PARAMETERS

f2lightfP

Specifies a light.
The number of lights depends on the implementation, but
at least eight lights are supported.
They are identified by symbolic names of the form %f3GL_LIGHTfP$i$
where 0 (<= $ i $ < %f3GL_MAX_LIGHTSfP.

Specifies a pointer to the value or values that parameter f2pnamefP
of light source f2lightfP will be set to.

DESCRIPTION

%f3glLightfP sets the values of individual light source parameters.
f2lightfP names the light and is a symbolic name of the form %f3GL_LIGHTfP$i$,
where 0 (<= i < %f3GL_MAX_LIGHTSfP.
f2pnamefP specifies one of ten light source parameters,
again by symbolic name.
f2paramsfP is either a single value or a pointer to an array that contains
the new values.
To enable and disable lighting calculation, call %f3glEnablefP
and %f3glDisablefP with argument %f3GL_LIGHTINGfP. Lighting is
initially disabled.
When it is enabled,
light sources that are enabled contribute to the lighting calculation.
Light source $i$ is enabled and disabled using %f3glEnablefP and
%f3glDisablefP with argument %f3GL_LIGHTfP$i$.
The ten light parameters are as follows:

%f3GL_AMBIENTfP

f2paramsfP contains four integer or floating-point values that specify
the ambient RGBA intensity of the light.
Integer values are mapped linearly such that the most positive representable
value maps to 1.0,
and the most negative representable value maps to -1.0.
Floating-point values are mapped directly.
Neither integer nor floating-point values are clamped.
The initial ambient light intensity is (0, 0, 0, 1).

%f3GL_DIFFUSEfP

f2paramsfP contains four integer or floating-point values that specify
the diffuse RGBA intensity of the light.
Integer values are mapped linearly such that the most positive representable
value maps to 1.0,
and the most negative representable value maps to -1.0.
Floating-point values are mapped directly.
Neither integer nor floating-point values are clamped.
The initial value
for %f3GL_LIGHT0fP is (1, 1, 1, 1); for other lights, the
initial value is (0, 0, 0, 0).

%f3GL_SPECULARfP

f2paramsfP contains four integer or floating-point values that specify
the specular RGBA intensity of the light.
Integer values are mapped linearly such that the most positive representable
value maps to 1.0,
and the most negative representable value maps to -1.0.
Floating-point values are mapped directly.
Neither integer nor floating-point values are clamped.
The initial value
for %f3GL_LIGHT0fP is (1, 1, 1, 1); for other lights, the
initial value is (0, 0, 0, 0).

%f3GL_POSITIONfP

f2paramsfP contains four integer or floating-point values that specify
the position of the light in homogeneous object coordinates.
Both integer and floating-point values are mapped directly.
Neither integer nor floating-point values are clamped.

The position is transformed by the modelview matrix when
%f3glLightfP is called (just as if it were a point),
and it is stored in eye coordinates.
If the $w$ component of the position is 0,
the light is treated as a directional source.
Diffuse and specular lighting calculations take the light's direction,
but not its actual position,
into account,
and attenuation is disabled.
Otherwise,
diffuse and specular lighting calculations are based on the actual location
of the light in eye coordinates,
and attenuation is enabled.
The initial position is (0, 0, 1, 0);
thus, the initial light source is directional,
parallel to, and in the direction of the $-z$ axis.

%f3GL_SPOT_DIRECTIONfP

f2paramsfP contains three integer or floating-point values that specify
the direction of the light in homogeneous object coordinates.
Both integer and floating-point values are mapped directly.
Neither integer nor floating-point values are clamped.

The spot direction is transformed by the inverse of the modelview matrix when
%f3glLightfP is called (just as if it were a normal),
and it is stored in eye coordinates.
It is significant only when %f3GL_SPOT_CUTOFFfP is not 180,
which it is initially.
The initial direction is (0, 0, -1).

%f3GL_SPOT_EXPONENTfP

f2paramsfP is a single integer or floating-point value that specifies
the intensity distribution of the light.
Integer and floating-point values are mapped directly.
Only values in the range [0,128] are accepted.

Effective light intensity is attenuated by the cosine of the angle between
the direction of the light and the direction from the light to the vertex
being lighted,
raised to the power of the spot exponent.
Thus, higher spot exponents result in a more focused light source,
regardless of the spot cutoff angle (see %f3GL_SPOT_CUTOFFfP, next paragraph).
The initial spot exponent is 0,
resulting in uniform light distribution.

%f3GL_SPOT_CUTOFFfP

f2paramsfP is a single integer or floating-point value that specifies
the maximum spread angle of a light source.
Integer and floating-point values are mapped directly.
Only values in the range [0,90] and the special value 180
are accepted.
If the angle between the direction of the light and the direction from the
light to the vertex being lighted is greater than the spot cutoff angle,
the light is completely masked.
Otherwise, its intensity is controlled by the spot exponent and the
attenuation factors.
The initial spot cutoff is 180,
resulting in uniform light distribution.

%f3GL_CONSTANT_ATTENUATIONfP

%f3GL_LINEAR_ATTENUATION fP

%f3GL_QUADRATIC_ATTENUATIONfP

f2paramsfP is a single integer or floating-point value that specifies
one of the three light attenuation factors.
Integer and floating-point values are mapped directly.
Only nonnegative values are accepted.
If the light is positional,
rather than directional,
its intensity is attenuated by the reciprocal of the sum of the constant
factor, the linear factor times the distance between the light
and the vertex being lighted,
and the quadratic factor times the square of the same distance.
The initial attenuation factors are (1, 0, 0),
resulting in no attenuation.

NOTES

It is always the case that %f3GL_LIGHTfP$i$ = %f3GL_LIGHT0fP + $i$.

ERRORS

%f3GL_INVALID_ENUMfP is generated if either f2lightfP or f2pnamefP
is not an accepted value.
%f3GL_INVALID_VALUEfP is generated if a spot exponent value is specified
outside the range [0,128],
or if spot cutoff is specified outside the range [0,90] (except for the
special value 180),
or if a negative attenuation factor is specified.
%f3GL_INVALID_OPERATIONfP is generated if %f3glLightfP is executed between
the execution of
%f3glBeginfP and the corresponding execution of %f3glEndfP.